Page:Popular Science Monthly Volume 12.djvu/710

690 was nearly smooth, and of moderate size. The skeleton most resembles that of the Lemurs. A nearly allied genus, belonging to the same family, is Hyopsodus. Limnotherium (Tomitherium) also is nearly related to the Lemurs, but shows some affinities with the South American marmosets. This genus had forty teeth. The brain was nearly smooth, and the cerebellum large, and placed mainly behind the cerebrum. The orbits are open behind, and the lachrymal foramen is outside the orbit. Other genera belonging to the Limnotheridæ are—Notharctos, Hipposyus, Microsyops, Palæacodon, Thinolestes, and Telmatolestes. Besides these, Antiacodon (Anaptomorphus), Bathrodon, and Mesacodon, should probably be placed in the same group. In the Diplacodon beds, or upper Eocene, no remains of Primates have yet been detected, although they will doubtless be found there. All the Eocene Primates known from American strata are low generalized forms, with characters in the teeth, skeleton, and feet, that suggest relationships with the Carnivores, and even with the Ungulates. These resemblances have led paleontologists to refer some imperfect specimens to both these orders.

In the Miocene lake-basins of the West, only a single species of the Primates has been identified with certainty. This was found in the Oreodon beds of Nebraska, and belongs to the genus Laopithecus, apparently related both to the Limnotheridæ and to some existing South American monkeys. In the Pliocene and Post-Pliocene of North America no remains of Primates have yet been found.

In the Post-Pliocene deposits of the Brazilian caves, remains of monkeys are numerous, and mainly belong to extinct species of Callithrix, Cebus, and Jacchus, all living South American genera. Only one extinct genus, Protopithecus, which embraced animals of large size, has been found in this peculiar fauna.

It is a noteworthy fact, that no traces of any Anthropoid apes, or indeed of any Old World monkeys, have yet been detected in America. Man, however, the highest of the Primates, has left his bones and his works from the arctic circle to Patagonia. Most of these specimens are clearly Post-Tertiary, although there is considerable evidence pointing to the existence of man in our Pliocene. All the remains yet discovered belong to the well-marked genus Homo, and apparently to a single species, at present represented by the American Indian.

In this rapid review of mammalian life in America, from its first known appearance in the Trias down to the present time, I have endeavored to state briefly the introduction and succession of the principal forms in each natural group. If time permitted, I might attempt the more difficult task of trying to indicate what relations these various groups may possibly bear to each other; what connection the ancient mammals of this continent have with the corresponding forms of the Old World; and, most important of all, what real progress